Robin-Robin preconditioned Krylov methods for fluid-structure interaction problems

In this work, we propose a Robin–Robin preconditioner combined with Krylov iterations for the solution of the interface system arising in fluid–structure interaction (FSI) problems. It can be seen as a partitioned FSI procedure and in this respect it generalizes the ideas introduced in [S. Badia, F. Nobile, C. Vergara, J. Comput. Phys. 227 (2008) 7027–7051]. We analyze the convergence of GMRES iterations with the Robin–Robin preconditioner on a model problem and compare its efficiency with some existing algorithms. The method is shown to be very efficient for many challenging fluid–structure interaction problems, such as those characterized by a large added-mass effect or by enclosed fluids. In particular, the possibility to solve balloon-type problems without any special treatment makes this algorithm very appealing compared to the computationally intensive existing approaches

Fluid-structure partitioned procedures based on Robin transmission conditions

In this article we design new partitioned procedures for fluid–structure interaction problems, based on Robin-type transmission conditions. The choice of the coefficient in the Robin conditions is justified via simplified models. The strategy is effective whenever an incompressible fluid interacts with a relatively thin membrane, as in hemodynamics applications. We analyze theoretically the new iterative procedures on a model problem, which represents a simplified blood-vessel system. In particular, the Robin–Neumann scheme exhibits enhanced convergence properties with respect to the existing partitioned procedures. The theoretical results are checked using numerical experimentatio

Virtual issue by COST Action BM1203 (EU-ROS) “Emerging concepts in redox biology and oxidative stress”

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Thermal Analysis of a Directly Grid-Fed Induction Machine with Floating Neutral Point, Operating under Unbalanced Voltage Conditions

Significant changes may occur in the thermal behavior of a directly grid-fed induction machine when subjected to unbalances in the voltage supply. This article studies and analyzes the thermal behavior of a low power, three-phase, squirrel-cage induction motor, connected in star configuration with floating neutral point, when subjected to different levels of unbalanced voltage. The dependence of the thermal motor behavior on the severity level of the unbalance is studied and analyzed. In addition to amplitude unbalances, this article focuses on the effects of phase unbalances, as well, which were not addressed in detail in previous published studies. Moreover, situations of mixed unbalance, where amplitude and phase unbalances occur simultaneously, are also studied. The finite element method was used to simulate the thermal behavior of the machine. The experimental setup consists of a three-phase programmable AC power supply, suitable to precisely emulate unbalanced conditions that may occur in real-scale power systems, supplying a 2.2 kW induction motor. Experimental data were acquired resorting to resistance temperature detectors PT100, placed in the machine phase whose supply current value changed the most. Finally, the simulation results are verified and critically discussed through experimentally obtained results.info:eu-repo/semantics/publishedVersio

Finite element method implemented in parallel algorithms applied in advective diffusive problems : a case study

Orientador: Luiz Fernando MilanezTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: Este trabalho tem como objetivo desenvolver códigos computacionais voltados apara a arquitetura de clusters a fim de resolver via Método dos Elementos Finitos um sistema acoplado de equações composto pelas Equações de Stokes e a Equação de Difusão Advceção. Devido às particularidades de cada uma delas, robustas estratégias computacionais devem ser empregadas de modo a se obter soluções numericamente estáveis e fisicamente realistas. O método de Galerkin é aqui utilizado na obtenção da forma ponderada residual para as equações de Stokes. Esta abordagem exige que a condição LBB seja respeitada ao se discretizar esta. Portanto, elementos de segunda ordem são utilizados no campo de velocidades e de ordem um são empregado no campo de pressão. Determinado os termos de velocidades, estes são então acoplados ao modelo difusivi-advectivo a fim de se obter a dispersão de uma pluma de poluentes ao longo domínio. Neste trabalho, os interesses estão voltados para situações físicas em que valores altos do número de Peclet ocorrem. Esta característica corrompe as soluções fornecidas pelo tradicional método de Galerkin, deste modo, empregou-se Streamline Upwind Petrov-Galerkin (SUPG). Este método, se caracteriza por ter a robustez e qualidade dos métodos clássicos upwind sem apresentar qualquer criticismo a respeito da difusão numérica artificial transversal ao escoamento comum deste último. De modo a aproveitar todas as informações sobre o campo de velocidade, o mesmo tipo de elemento utilizado na discretização deste foi empregado no modelo difusivo advectivo. Esta escolha impõe dificuldades adicionais, uma vez que funções upwind distintas devem ser utilizadas sobre nós do vértice e aqueles localizados sobre as arestas. Realizada a discretização espacial do modelo, o método de Crank-Nicolson foi empregado na discretização temporal. Esta escolha se deve as características desse método, de ser incondicionalmente estável e possuir ordem de convergência quadrática. Ao final deste trabalho, pretende-se ter além uma robusta estrutura de algoritmos voltados para cluster a fim de resolver os modelos descritos, pretende-se também realizar o estudo de dois cenários para o modelo difusivo advectivo sobre a região de estudoAbstract: This work aims to develop computational codes aimed at the cluster architecture in order to solve via a Finite Element Method a coupled system of equations composed of the Stokes Equations and the Diffusion Equation Advance. Due to the particularities of each of them, robust computational strategies must be employed in order to obtain numerically stable and physically realistic solutions. The Galerkin method is used here to obtain the residual weighted form for the Stokes equations. This approach requires that the LBB condition be respected by discretizing it. Therefore, second-order elements are used in the velocity field and one order is employed in the pressure field. Once the velocity terms have been determined, they are then coupled to the diffusive-advective model in order to obtain the dispersion of a pollutant plume over the domain. In this paper, interests are focused on physical situations in which high Peclet numbers occur. This feature corrupts the solutions provided by the traditional Galerkin method, thus using Streamline Upwind Petrov-Galerkin (SUPG). This method is characterized by having the robustness and quality of classical methods upwind without presenting any criticism regarding artificial numerical diffusion transverse to the common flow of the latter. In order to take advantage of all the information about the speed field, the same type of element used in the discretization of this was used in the advective diffusive model. This choice imposes additional difficulties, since distinct upwind functions must be used on nodes of the vertex and those located on the edges. After the spatial discretization of the model, the Crank-Nicolson method was used in temporal discretization. This choice is due to the characteristics of this method, to be unconditionally stable and to have order of quadratic convergence. At the end of this work, we intend to have a robust structure of cluster-oriented algorithms in order to solve the described models, we also intend to study two scenarios for the advective diffusive model over the study regionDoutoradoTermica e FluidosDoutor em Engenharia Mecânica33003017CAPE

A fitting algorithm for random modeling the PLC channel

The characteristics of the power-line communication (PLC) channel are difficult to model due to the heterogeneity of the networks and the lack of common wiring practices. To obtain the full variability of the PLC channel, random channel generators are of great importance for the design and testing of communication algorithms. In this respect, we propose a random channel generator that is based on the top-down approach. Basically, we describe the multipath propagation and the coupling effects with an analytical model. We introduce the variability into a restricted set of parameters and, finally, we fit the model to a set of measured channels. The proposed model enables a closed-form description of both the mean path-loss profile and the statistical correlation function of the channel frequency response. As an example of application, we apply the procedure to a set of in-home measured channels in the band 2-100 MHz whose statistics are available in the literature. The measured channels are divided into nine classes according to their channel capacity. We provide the parameters for the random generation of channels for all nine classes, and we show that the results are consistent with the experimental ones. Finally, we merge the classes to capture the entire heterogeneity of in-home PLC channels. In detail, we introduce the class occurrence probability, and we present a random channel generator that targets the ensemble of all nine classes. The statistics of the composite set of channels are also studied, and they are compared to the results of experimental measurement campaigns in the literature

Law and social emancipation

El siguiente trabajo pretende hacer una crítica a la forma como tradicionalmente se concibe el derecho en las democracias liberales: una construcción racional en la que la ideología ha sido superada y así mismo las luchas entre clases con intereses antagónicos no tienen lugar. Tiene como fin vislumbrar cómo el derecho y las instituciones jurídicas tal como se conocen hoy en día son una producción ideológica y responden a intereses políticos claros. Esta crítica va a ser abordada desde el análisis de la tesis de Francis Fukuyama en la que expone el ser humano mediante la democracia liberal ha arribado al fin de la historia. Por otro lado, se analizará el concepto de lucha de clases como motor de la historia; se dará un paso por el concepto de estado de excepción en Ágamben y en última medida se analizará el papel de las normas laborales en los intereses de clase como base de la labor legislativa.The next paperwork pretends to make a critic to the way the law in the liberal democracies is traditionally conceived: a rational construction in which the ideology has been overcome and also the struggles among social classes with antagonistic interests have no place. It aims to discern how law and legal institutions, as are known nowadays, are a ideological production and respond to clear political interests. This critic is going to be addressed from the analysis of Francis Fukyama’s thesis, where he exposes mainly that the human been through liberal democracy has arrived at the end of the history. On the other hand, it will be analyzed the class struggle as the motor of history; it will be given a step through the concept of state of exception in Agamben and in last measurement will be analyzed the role of labor standards in the class interests as the base of the legislative work in modernity